1. Field of the Invention
The present invention relates to a rare gas discharge fluorescent lamp device for use with an information device such as a facsimile, a copying machine or an image reader.
2. Description of the Prior Art
In recent years, the performances of information terminal devices such as a facsimile, a copying machine and a image reader have been improved together with advancement of the information-oriented society, and the market of such information devices is rapidly expanding. In developing information devices of a higher performance, a light source unit for use with such information devices is required to have a higher performance as a key device thereof. Conventionally, halogen lamps and fluorescent lamps have been employed frequently as lamps for use with such light source units. However, since halogen lamps are comparatively low in efficiency, fluorescent lamps which are higher in efficiency are used principally in recent years.
However, while a fluorescent lamp is high in efficiency, it has a problem that characteristics thereof such as an optical output characteristic vary in accordance with a temperature since discharge from vapor of mercury is utilized for emission of light. Therefore, when a fluorescent substance is used, either the temperature range in use is limited, or a heater is provided on a wall of a tube of the lamp in order to control the temperature of the lamp. However, development of fluorescent lamps having stabilized characteristics are demanded eagerly for diversification of locations for use and for improvement in performance of devices. From such background, development of a rare gas discharge fluorescent lamp which makes use of emission of light based on rare gas discharge and is free from a change in temperature characteristic is being proceeded as a light source for an information device.
FIGS. 26 and 27 show an exemplary one of conventional rare gas discharge fluorescent lamp devices which is disclosed, for example, in Japanese Patent Laid-Open No. 63-58752, and wherein FIG. 26 is a constructional view showing a transverse section of a rare gas discharge fluorescent lamp and an entire construction of the device, and FIG. 27 is a vertical sectional view of the lamp. Referring to the figures, reference numeral 1 denotes a bulb in the form of an elongated hollow rod, which is made of quartz or hard or soft glass. A fluorescent layer 2 is formed on an inner face of the bulb 1, and rare gas X consisting of at least one of xenon, krypton, argon, neon, helium and so forth is enclosed in the bulb 1. A pair of inner electrodes 3a and 3b having different polarities from each other are located at the opposite end portions within the bulb 1. The inner electrodes 3a and 3b are individually connected to a pair of lead wires 4 which extend in an airtight condition through walls of the end portions of the bulb 1. Further, an outer electrode 5 in the form of a belt is provided on an outer face of a side wall of the bulb 1 and extends in an axial direction of the bulb 1.
The inner electrodes 3a and 3b are connected by way of the lead wires 4 to a high frequency inverter 6 serving as a high frequency power generating device, and the high frequency inverter 6 is connected to a dc power source 7. Then, the outer electrode 5 is connected to the high frequency inverter 6 such that it may have the same polarity as the one inner electrode 3a.
Operation is described subsequently. With the rare gas discharge fluorescent lamp device having such a construction as described above, if a high frequency power is applied across the inner electrodes 3a and 3b by way of the high frequency inverter 6, then glow discharge will take place between the inner electrodes 3a and 3b. The glow discharge will excite the rare gas within the bulb 1 so that the rare gas will emit peculiar ultraviolet rays therefrom. The ultraviolet rays will excite the fluorescent layer 2 formed on the inner face of the bulb 1. Consequently, visible rays of light are emitted from the fluorescent layer 2 and discharged to the outside of the bulb 1.
Meanwhile, another rare gas discharge fluorescent lamp is disclosed as an example in Japanese Patent Laid-Open No. 63-248050. The lamp employs such a hot cathode electrode as disclosed, for example, in Japanese Patent Publication No. 63-29931 in order to eliminate the drawback of a cold cathode rare gas discharge lamp that the starting voltage is high. The rare gas discharge fluorescent lamp can provide a comparatively high output power because its power load can be increased. However, it can obtain only a considerably low efficiency and optical output as compared with a fluorescent lamp based on mercury vapor.
However, conventional rare gas discharge fluorescent lamps cannot readily attain a sufficiently high brightness as compared with fluorescent lamps employing mercury because fluorescent substance is excited to emit light by ultraviolet rays generated by rare gas discharge, and therefore, a rare gas discharge fluorescent lamp in high efficiency has been awaited. Further, since a conventional lamp adopts a hot cathode electrode, an extra power supply is not necessary for preheating the cathode electrode.